Incandescent lamps are probably still the most common type of lamp in use. However, the high heat output and low efficiency disadvantages of incandescent lamps are well known. These disadvantages have caused the use of electronic lamps, such as fluorescent lamps and metal-vapor discharge lamps, to become more and more widespread.
However, electronic lamps have different disadvantages. A special circuit, generally referred to as a ballast, is required to start the lamps. One common ballast is simply a transformer. However, a ballast transformer is bulky and heavy and is generally suited for use only in places where size and weight is not particularly significant, for example, in ceiling mounted locations, such as in offices and in hanging "shop" lights.
Electronic lamps are not limited to use in ceiling mounted locations. It is highly desirable to use electronic lamps to replace incandescent lamps in many locations, such as conventional table, floor, and column lighting devices in the home. Considerable savings in energy costs can be achieved in commercial lodging facilities, such as hotels and motels, by replacing incandescent lighting devices with electronic lighting devices. In addition, considerable reduction in the overall use of energy can be achieved by such replacement in homes, commercial facilities, and offices.
However, ballast transformers are generally unsuited for use in conventional table, floor, and column lighting devices because of the size and weight of the transformer. In addition, ballast transformers represent an inductive load which adversely affects the power factor. Therefore, circuits have been designed for starting and operating electronic lamps. For example, see U.S. Pat. Nos. 4,277,728; 4,525,650; 4,544,863; 4,572,989; 4,585,974; 4,851,739; 4,972,124; 5,111,380; 5,138,235; 5,166,579; 5,179,326; 5,191,262; 5,214,355; 5,258,692; and 5,262,699; the teachings of all of which are hereby incorporated herein by reference.
In addition, some existing lighting fixtures, such as overhead ceiling panel lighting, may be conveniently modified to accommodate an improved ballast circuit. However, many lighting fixtures, such as table, floor and column lamps, cannot be so modified, for reasons such as the person-hour costs involved in the modification, size constraints, and appearance. Therefore, there is a need for a ballast for electronic lamps which can be used to retrofit existing light fixtures for use with electronic lamps without requiring modification of the existing light fixture.
In addition, there is a need for a ballast circuit for electronic lamps which provides for starting and operating both fluorescent lamps and metal-vapor discharge lamps, without the need for any changes in the circuit.
Further, there is a need for a ballast circuit for electronic lamps which provides for high efficiency and a high power factor.